EL SEGUNDO, Calif. — They looked tired, a step slow. Maybe even two.

Then the third quarter started and the Lakers snapped to life at Staples Center.

They had just enough in them to fend off the Golden State Warriors, 103-100, in a defensively charged game of the NBA’s play-in tournament Wednesday.

The Lakers were officially stamped the Western Conference’s seventh-seeded team and play second-seeded Phoenix in the first round of the playoffs. Game 1 of the best-of-seven series is Sunday in Phoenix.

Had the Lakers lost, they’d face a win-or-you’re done game against Memphis on Friday. They now get a few days of rest, coupled with some practice time, as they game plan for the Suns, who had a surprisingly strong season.

It took a 34-foot heave from LeBron James to make it official.

His off-balance 3-pointer as the shot clock expired gave the Lakers a 3-point lead with 58.2 seconds left. It was a scattershot play from the start. Kentavious Caldwell-Pope was in trouble near the basket and flung the ball out top to James, who had just enough time to snare the ball and hoist the go-ahead shot while falling away.

Just a few minutes earlier, James fell hard to the court after a foul from Warriors forward Draymond Green, who poked James in the eye. James appeared to tell athletic trainers that he had trouble seeing but stayed in the game.

It made his last-minute shot that much more impressive. In fact, James said he saw “three rims” as he lofted it.

“So I just aimed for the middle one,” he said.

Teammate Anthony Davis overcame a poor first half to finish with 25 points and 12 rebounds in 42 minutes. But the talk after the game was about James’ long-distance heave.

“I think they need to poke LeBron in the eye a lot more,” Davis joked. “Great shot.”

James’ shot concluded the scoring, as Warriors guard Jordan Poole missed a three-point shot and then Curry couldn’t corral an off-target inbounds pass from Kent Bazemore in the final seconds.

James finished with a triple-double — 22 points, 11 rebounds and 10 assists.

There were some ugly numbers for the Lakers as they trailed by 13 at halftime. Davis had hit 2 of 12 shots. Dennis Schröder was one for nine. James was one for seven.

“We had to be more physical. That first half, they did whatever they wanted,” Davis told Spectrum SportsNet. “We came in the locker room and said the game isn’t over.”

He was right.

Alex Caruso was the Lakers’ only reliable scoring option in the first half and finished with 14 points in one of his best games as a pro. He also added a big assist on a pass to Davis for a dunk that put the Lakers ahead, 100-98, with 1:31 to play.

“He’s just very smart, knows what he wants to do. Always in the right place at the right time,” James said, adding that Caruso’s contributions aren’t always obvious…but they were Wednesday. “Tonight, they definitely showed up in the box score.”

The Lakers didn’t have a lead until a minute into the fourth quarter when James fed Kyle Kuzma for a quick hook shot down low and an 81-79 edge.

Stephen Curry scored 37 points and Andrew Wiggins added 21 for Golden State.

The Lakers (43-30) now face the Suns (51-21), who exceeded expectations and finished one game behind Utah for first place in the West. The Lakers went 1-2 against Phoenix during the regular season, but won impressively the last time they played, 123-100, behind Davis’ 42 points and 12 rebounds on May 9.

Davis did not play the first two games against Phoenix, which the Suns won by 17 and 10 points in March.